1. Field of the Invention
The present invention relates generally to electrical wiring devices, and particularly to an electrical wiring device with a rigid substantially non-deformable housing.
2. Technical Background
Any structure that is equipped with electric service typically includes one or more electric circuits installed throughout. An electric circuit is comprised of electrical wiring that is disposed between the panel box and locations where service is desired. Moreover, the wiring interconnects various kinds of electrical wiring devices—such as electrical receptacles—that are disposed at the various service locations. In addition to electrical receptacle devices, protective electrical wiring devices such as GFCIs, AFCIs, TVSS devices and the like often include one or more electrical outlets that provide access to AC power. Moreover, there are devices that are configured to mix-and-match electrical outlets with other electrical functions such as USB ports, low voltage ports, night lights, dimming or fan speed controls, occupancy sensing, and/or remote communication devices.
In any event, once an electrical wiring device is properly terminated by the electrical wiring, it is disposed in a device box and a cover plate is installed. Electrical wiring devices often have a screw hole disposed at a central portion thereof; the screw hole is configured to receive a cover plate screw that fastens the cover plate to the wiring device. As those skilled in the art will appreciate, the cover plate “completes the enclosure” by preventing user access to the interior of the device box so that no energized wires or electrical conductors are accessible to a user. In other words, the cover plate serves an important safety function by preventing inadvertent shock or electrocution by touching exposed wiring.
Another shock/electrocution safety issue relates to the propensity of toddlers and young children to insert various objects (such as paper clips, screwdriver blades, etc.) into the receptacle contact openings of a wiring device. In order to prevent this scenario from playing out, shutter devices are typically installed within electrical receptacles. Specifically, shutters are configured to allow corded plug blades from being inserted while, at the same time, preventing foreign objects from being inserted into the receptacle openings and making contact with live contacts disposed therewithin.
A problem arises during a sequence of events that has occurred during device installation. As shown in FIGS. 1A-1C, a device box has been attached to a mounting surface such as a wall stud, ceiling joist, or counter-top. Wires are routed through openings in the device box, their ends sticking out of the open front face of the box. Sheet rock or some overlay material is installed having a cutout. The wire ends extend from the cutout and get fastened to the wiring device. With all wire ends terminated, the wiring device is pushed through the cutout into device box where it is secured to the device box with mounting screws. Then a cover plate is attached to the wiring device using the central screw.
Referring to FIGS. 1A-1C, diagrammatic depictions of electrical wiring device installations are shown. In FIG. 1A, a device box 2 is disposed in an appropriately sized opening in a mounting surface MS (e.g., a wall) and is essentially flush with it. The mounting ears 1-1 of the electrical wiring device 1 are also flush with the mounting surface MS. The device 1 includes a center screw member 1-3 that holds the cover and the back body portion together. Moreover, the center screw 1-3 includes a central tap that is configured to accommodate the screw for the cover plate 3. In FIG. 1B, the opening in the mounting surface MS is too large and, moreover, the device box is too deep within the mounting surface. In this case, there is gap “x” between the wall or mounting surface and the device box such that a force, or stress, is applied to the mounting ears 1-1 in the manner shown. There is another gap “y” between the cover plate 3 and the top surface of the electrical wiring device 1.
Referring to FIG. 1C, the significance of the gaps (x, y) caused by a misaligned or poor installation is shown. As noted above, the cover plate 3 is attached to the wiring device 1 by a center screw. The center screw applies a force “F” of about forty (40) pounds to the center of the wiring device. When the mounting ears are fastened to the device box 2, an opposing force (F/2), or about half of the center force, is applied at each end of the device 1 where the mounting ears are fastened to the device box 2. As a result of the stresses applied by the installation misalignment shown in FIG. 1B, the front cover 1-4 of the device 1 can become distorted so that the shutter elements 1-5 become jammed or misaligned with the plug blade apertures formed in the front cover 1-4.
In reference to FIGS. 2A-2C, diagrammatic depictions illustrating the forces applied to the wiring devices depicted in FIGS. 1A-1C are shown. FIGS. 2A-C are exaggerated somewhat to clearly show the types of forces that can be applied to the device if it is misaligned or installed incorrectly. To be specific, bending and/or twisting forces can be applied to the electrical wiring device 1 depending on the way the device and the device box are installed. As noted above, when these bending and/or twisting forces are applied to the electrical wiring device, the shape of the electrical wiring device housing can be distorted and damaged.
Referring back to FIG. 1C, when the electrical wiring device housing is distorted and/or damaged from the aforementioned stresses, the user may attempt to insert a corded plug blade set into the receptacle outlet only to find that the tamper-resistant shutters have been misaligned, and hence, jammed by the applied forces. When the installation misalignment is severe, the damage can result in the loss of both structural and electrical integrity. This condition could further result in poor electrical connections.
In one approach that has been considered, the plastic cover portion and back body portion are welded, snapped, or otherwise fastened together to provide additional rigidity. However, these approaches have been found to be generally unreliable due to plastic creep, cracking, manufacturing variables, or environmental conditions. In other words, the relentless forces applied by the central attachment screw and the mounting ear screws is often greater than the strength of the plastic materials used to fasten the cover portion to the back body.
In another approach that has been considered, the conductive ground strap is wrapped around the back body of the wiring device. One drawback to this approach is that it is not cost effective (specifically, this approach results in a relatively thick wiring device and it also requires a ground buss to be formed between the rear exterior portion of the strap to the receptacle ground terminals). Moreover, the wrap-around strap is no guarantee that the reliability issues due to plastic creep, cracking, manufacturing variables, or environmental conditions will not occur nonetheless.
What is needed is a reliable and cost-effective wiring device that can withstand the forces applied by device installation misalignments. What is also needed is a structural element—in an electrical wiring device—that can contend with and resist bending and twisting forces that are often applied device installation misalignments. What is further needed is a structural element that is configured to provide enough rigidity to the electrical wiring device in a plane substantially parallel to the cover plate.